The present invention relates to a printed wiring board, more particularly, a double-sided printed wiring board or a multilayer printed wiring board.
A printed wiring board having an electromagnetic wave shielding layer provided through an insulating layer is well known from Japanese Patent Laid-open No. 213,192/87. The printed wiring board 9 disclosed in this Japanese Patent Laid-open comprises, as shown in FIG. 3, an insulating sheet 1, printed wiring circuits 2 formed on both surface of the insulating sheet 1, an insulating layer 4 provided on a part of the printed wiring circuits 2, an electromagnetic wave shielding layer 5 provided on the insulating layer 4 and a part of the printed wiring circuit 2 and a solder resist layer 6 provided on the shielding layer 5.
The printed wiring board 9 further comprises a connecting through hole portion 7 including a plated through hole 8 provided in the insulating sheet 1, so that the connecting through hole portion 7 and component connecting land (not shown) are not covered with the electromagnetic wave shielding layer 5.
In such a conventional printed wiring board 9 having the electromagnetic wave shielding layer 5, the shielding layer 5 does not cover the connecting through hole portion 7, so that the electromagnetic wave of passive noise or active noise affects on the printed wiring board through the connecting through hole portion 7.
Moreover, provision of the connecting through hole portion 7 including component connecting land (not shown) leads to a division or discontinuity of the electromagnetic wave shielding layer 5, so that an effective aria of the shielding layer becomes decreased and thus sufficient shielding effect can not be obtained.